Attempts at immune activation and restoration in the past have utilized bone marrow transplantation or lymphocyte transfers (H. C. Lane et al., Ann. Internal Med. 113: 512-19 (1990)), immunomodulating agents such as immuthiol (J. M. Lang et al., Lancet 24: 702-06 (1988)) or isoprinosine (C. Pedersen et al., N. Engl. J. Med. 322: 1757-63 (1990)), and recombinant cytokines such as interferon alpha (IFN-.alpha.) and IL-2. H. C. Lane et al., Ann. Intern. Med. 112: 805-11 (1990); H. C. Lane et al., J. Biol. Response Mod. 3, 512-16 (1984); D. H. Schwartz et al., J. Acquir. Immune Defic. Syndr. 4, 11-23 (1991); P. Mazza et al., Eur. J. Haematol. 49: 1-6 (1992); H. W. Murray et al., Am. J. Med. 93: 234 (1992); H. Teppler et al., J. Infect. Dis. 167: 291-98 (1993); P. Volberding et al., AIDS Res. Hum. Retroviruses 3: 115-24 (1987). These studies have resulted in minimal or only transient immune system restoration.
The use of biologic response modifiers in general, and of IL-2 in particular, is an active area of clinical research. Interleukin-2 is a T cell-derived lymphokine with a number of immunomodulating effects including activation, as well as induction of proliferation and differentiation, of both T and B lymphocytes. K. A. Smith, Science 140: 1169-76 (1988). Exogenous IL-2 has been shown in vitro to increase the depressed natural killer cell activity and cytomegalovirus-specific cytotoxicity of peripheral blood mononuclear cells from patients with AIDS, as well as to increase IFN-.gamma. production by lymphocytes from patients with AIDS. A. H. Rook et al., J. Clin. Invest. 72: 398-403 (1983); H. W. Murray et al., loc. cit. 76: 1959-64 (1985).
IL-2 given by high dose infusion has been employed in the treatment of renal cell carcinoma and melanoma. J. Nat'l Cancer Inst. 85(8): 622-32 (1993). For example, doses of 36 million international units (MU) given continuously over a period of 24 hours has been used in the treatment of cancer (18 MU is equivalent to about 1 mg protein). Lancet 340: 241 (1992). The use of high doses of IL-2 generally is not well tolerated by patients, however, and side effects are more pronounced at such high levels.
Subcutaneous administration of IL-2 has been evaluated extensively in patients with metastatic cancer, although most often in conjunction with alpha interferon. Our current data suggest that the maximum tolerated dose of subcutaneous IL-2 given over a five day course of therapy is about 21 MU/day. Most previous trials used a four week regimen of dosing. The highest subcutaneous dose of IL-2 delivered in a single agent setting was delivered in an intrapatient dose escalation trial where four patients tolerated doses equal to or in excess of 24 MU/m2/day. These patients had already received more than one month of IL-2, so these doses were tolerable in spite of chronic dosing. Whitehead et al., Cancer Res 50: 6708 (1990). A similar trial delivered doses in the range of 18 MU/patient on a five day basis followed by lower doses for prolonged periods. Sleijfer et al., J. Clin. Oncol. 10:1119 (1992); Lissoni et al., Eur. J. Cancer 28: 92 (1992). Other trials have used lower dose IL-2 regimens with similar toxicities. Urba et al., Cancer Res. 50: 185 (1990); Stein et al., Br. J. Cancer 63: 275 (1991); Atzpodien et al., Mol. Biother. 2:18 (1990). Thus, subcutaneous dose levels of IL-2 in the range of 18-24 MU/day have been reasonably well tolerated over one month of therapy.
Subcutaneous IL-2 is poorly absorbed, however, and local reactions can be dose-limiting. McElrath et al., Proc. Nat'l Acad. Sci., USA 87: 5783 (1990), suggest that locally high concentrations of IL-2 can have systemic effects as assessed by activation of lymphocytes remote from the site of injection. Further, in HIV seronegative populations, subcutaneous IL-2 at tolerable doses has led to increases in lymphocyte counts and improved cytotoxicity as assessed by NK and LAK activity. Most of the patients treated with these regimens had metastatic cancer and the additional observation of objective tumor responses suggests that the immune activation was clinically important.
Other researchers are evaluating IL-2 in the treatment of other diseases, including HIV infection. The use of lower doses of IL-2 in a continuous therapy regime has been disclosed by Yarchoan et al., U.S. Pat. No. 5,026,687. More specifically, Yarchoan et al. teach the use of the anti-retroviral agent ddI in combination with IL-2 administered continuously at a dosage between 25,000 to 1 million international units (MU) per day, for a period of three months. While Yarchoan et al. predict that "beneficial results" will accompany the combined ddI/IL-2 regimen, they do not attribute these results to IL-2 per se. Moreover, dosages at this lower level have been shown to cause an initial increase in CD4 level that was transient in nature: that is, CD4 levels returned to baseline within 6 months after the completion of the treatment.
Many researchers feel that the use of IL-2 is contraindicated in patients with HIV infection due to its potential to activate HIV. No method of treatment of HIV with IL-2 has been disclosed which results in a sustained response or which yields long-term beneficial results.
Cells that have been stimulated to actively synthesize DNA are susceptible to transduction by gene transfer therapy. Present methods of gene therapy require a complicated, in vitro transformation. More specifically, cells are removed from a patient, activated in vitro, and used to establish cell lines which are then gene-transduced in vitro and re-implanted in the patient. This procedure is expensive, and its success its limited due to the potential of failure at each of the steps of activating the cells, effecting the transduction, and implanting the cells in the patient for expression.
Attempts at using retroviral vectors to effect in vivo gene transfer have been limited. Retroviruses will only integrate stably into target cells that are actively synthesizing DNA. This integration must occur before retroviral gene expression can be effected. Because only a fraction of cells are actively producing DNA at any giving time, such in vivo gene transfer methods have shown little success.